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Home>Article>Java> What are the ways to remove duplicates from List collections in Java?

What are the ways to remove duplicates from List collections in Java?

王林
王林 forward
2019-11-27 15:11:13 4643browse

What are the ways to remove duplicates from List collections in Java?

Duplication removal method:

1. Through the characteristics of the set collection, the uniqueness of the set elements

public static List heavyListMethod01(List list){ Set set=new HashSet(list); //Set set1=new TreeSet(list); List alist=new ArrayList(); for (Object o:set) { alist.add(o); } return alist; }

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Use the characteristics of the set collection, the uniqueness of the elements AddAll(Collection c)

public static List heavyListMethod02(List list){ List newList=new ArrayList(); newList.addAll(new HashSet(list)); return newList; }

2. Use the list method contains method to remove duplicates

public static List heavyListMethod03(List list){ List alist=new ArrayList(); for (Object o:list) { if(!(alist.contains(o))){ alist.add(o); } } return alist; }

3. By traversing, and then using the remove method to remove duplicate elements

public static List heavyListMethod04(List list){ for (int i=0;i
      
4. (jdk1.8) Call the stream method to convert the list For a stream, remove duplicate elements in the stream through distinct (internally based on the equals() method)

      
public static List heavyListMethod05(List list){ list = list.stream().distinct().collect(Collectors.toList()); return list; }
      
Test verification:

      
public static void main(String[] args) { List list=new ArrayList(); list.add(1); list.add(2); list.add(5); list.add(2); list.add(3); list.add(1); list.add(4); List list1 =heavyListMethod01(list); System.out.println("1----"+list1);//[1, 2, 3, 4, 5] List list2 =heavyListMethod02(list); System.out.println("2----"+list2);//[1, 2, 3, 4, 5] List list3 =heavyListMethod03(list); System.out.println("3----"+list3);//[1, 2, 5, 3, 4] List list4 =heavyListMethod04(list); System.out.println("4----"+list4);//[1, 2, 5, 3, 4] List list5 =heavyListMethod05(list); System.out.println("5----"+list5);//[1, 2, 5, 3, 4] }

      
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